This invention relates to chemically-modified group B polysaccharides of Neisseria meningitidis. This invention also provides vaccines in which the respective modified polysaccharides are conjugated to a protein carrier, and the like.
Meningitis caused by group B N. meningitidis and E. coli K1 remain major world health problems. Group B meningitis occurs in both endemic and epidemic situations and accounts for approximately half of all recorded cases of meningococcal meningitis, while K1-positive E. coli are the leading cause of meningitis in neonates. Currently there is no vaccine commercially available against disease caused by group B meningococci and E. coli K1. This is in large part due to the fact that the group B meningococcal polysaccharide (GBMP) is only poorly immunogenic in humans. This poor immunogenicity of native GBMP and resulting immune tolerance has been postulated to be due to the presence of a common epitope in human and animal tissue. There are some recently reported candidate vaccines based on complexes of the GBMP with outer membrane proteins, but, as yet, there is no clear evidence of their efficacy in humans.
Recently, a new concept of a vaccine based on a synthetic chemically modified (N-propionylated) group B polysaccharide-protein (N-Pr-GBMP-protein) conjugate has been developed. The vaccine induces in mice high titers of IgG antibodies which are not only protective, but also cross-react with unmodified GBMP (i.e. N-acetyl-GBMP). This concept is described and claimed in U.S. Pat. No. 4,727,136, issued Feb. 23, 1988 to Harold J. Jennings, et al.
It has been inferred that a vaccine which raises cross-reactive antibodies, such as that described in U.S. Pat. No. 4,727,136, could only be successful at the expense of breaking immune tolerance. This hypothesis is legitimized by the identification of a common epitope consisting of a chain of xcex1-(2-8)-linked sialic acid residues (with a minimum requirement of ten residues) in both the native N-Ac-GBMP and in human and animal tissue (Jennings, Contrib. Microbiol. Immunol. Basel, Karger, 1989, Vol. 10, 151-165). These polysialosyl chains function as developmental antigens and have for the most part been associated with the fetal state in embryonic neural cell adhesion (Finne et al, Biochem. Biophys. Res. Commun., 1983, 112, 482). During post-natal maturation, this antigen is down-regulated (Friedlander et al, J. Cell Biol. 1985, 101, 412) but is expressed in mature humans during the regeneration of diseased muscles (Cashman et al, Ann. Neuron., 1987, 21, 481) in tumor cells (Roth et al, Proc. Natl. Acad. Sci., 1988, 85, 299) and in natural killer (NK) and CD3+T cells (Husmann et al, Eur. J. Immunol., 1989, 19, 1761. Although the consequences of breaking tolerance to these fetal antigens have not yet been established, it is desirable to develop vaccines which have reduced immunogenicity for human epitopes.
Therefore, an object of the present invention is to develop modified group B meningococcal polysaccharides which are immunogenic yet induce antibodies which have reduced cross-reactivity with native epitopes of the host. It is another object to provide polysaccharide-protein conjugates which comprise these modified polysaccharides. Another object of this invention is to provide vaccines having immunogenic properties which exhibits substantially reduced cross-reactivity with GBMP.
The present invention generally provides chemically-modified group B polysaccharides of Neisseria meningitidis. The present invention also provides for vaccines in which the respective modified polysaccharides are conjugated to a protein carrier.
Specifically, this invention provides for unsaturated group B N-acyl derivative polysaccharides of N. meningitidis, conjugates of the unsaturated N-acyl derivative polysaccharide covalently bound to proteins, pharmaceutical compositions comprising conjugate molecules of N. meningitidis unsaturated N-acyl derivative polysaccharides, and the use of these compositions as vaccines.
In one aspect of the invention, there is provided a modified B polysaccharide of N. meningitidis having sialic acid residue N-acetyl (C2) groups replaced by an unsaturated C3-5 acyl group.
In another aspect, there is provided an antigenic conjugate comprising unsaturated C3-5 N-acyl derivative polysaccharides conjugated to an immunologically suitable protein, having enhanced immunogenicity compared to native polysaccharides with reduced inducement of cross-reactive antibodies.
In a further aspect, there is provided a vaccine comprising the unsaturated N-acyl derivative polysaccharide-protein conjugate in association with a suitable carrier or diluent. The vaccines of the invention may also comprise a therapeutically effective amount of an adjuvant suitable for human use, for example aluminum phosphate, aluminum hydroxide or stearyl tyrosine.
In a yet further aspect, there is provided a method of immunizing mammals against N. meningitidis and E. coli K1 infections, which method comprises administering parentally to mammals subject to such infections, including humans, an immunologically effective amount of the vaccine of the invention. The vaccine is typically administered in an amount of about 1 to 50 micrograms per kilogram body weight, for example 5 to 25, micrograms per kilogram body weight.
In yet another aspect, the invention provides serum and a gamma globulin fraction capable of protection against meningitis caused by group B N. meningitidis and E. coli K1. The fraction is produced by immunizing a mammal with a vaccine of the invention and preferably separating the gamma globulin fraction from the immune serum. The fraction is then administered to an individual to provide protection against or to treat on-going infection caused by the above organisms. From this, it will be appreciated that the immunogenic vaccine conjugates of the invention will be a source of therapeutic antiserum in light of their favorable immunogenicity with minimal inducement of GBMP cross-reactive antibodies. The conjugates of the invention will also be useful for raising monoclonal antibodies and, possibly, antiidiotype antibodies.
We have found that most of the bactericidal and protective antibodies induced by the N-Pr-GBMP-protein conjugate described in the above-referred to Jennings et al U.S. Pat. No. 4,727,136 are not associated with the GBMP cross-reactive antibodies. In fact, most of the protective activity is contained in an N-Pr-GBMP-specific antibody population which does not cross-react with GBMP. In light of this, it is believed that the N-Pr-GBMP mimics a unique bactericidal epitope on the surface of group B meningococci.
The present invention is based on the discovery that it is possible to synthesize chemically modified GBMP""s which mimic the bactericidal epitope and which, in their conjugated form, not only exhibit enhanced immunogenicity but also avoid substantially the inducement of antibodies that do cross-react with GBMP.
In arriving at the present invention, different chemically modified GBMP""s have been synthesized and conjugated individually to protein, followed by injection of the conjugates into mice and the effects compared to those produced by the N-Pr-GBMP protein conjugate. Surprisingly, it has now been found that the presence of an unsaturated bond in the N-acyl results in particularly immunogenic conjugates
These and other features of the invention will be better understood through a study of the following detailed description of a specific embodiment of the invention. The scope of the invention is limited only through the claims appended hereto.
This invention generally provides novel group B Neisseria meningitidis unsaturated N-acyl derivative polysaccharides, novel conjugates of the group B unsaturated N-acyl derivatives, pharmaceutical compositions comprising conjugate molecules of group B Neisseria meningitidis unsaturated N-acyl derivative polysaccharide fragments covalently bound to proteins, and the use of these compositions as vaccines.
The present invention relates to group B N. meningitidis unsaturated N-acyl derivative polysaccharides of Formula (I): 
wherein R1 is a C2-C4 unsaturated alkyl group comprising at least one double bond.
In one embodiment of the invention, R1 of Formula I has three, or four carbons and two nonadjacent double bonds.
In a further embodiment of the invention, R1 of Formula I is two, three, or four carbons, and the carbon most distant from the acyl carbon is bound through a double bond.
Specific, but not limiting examples of modified group B meningococcal polysaecharide N-acyl derivative polysaecharides of Formula I useful in the present invention include the following: 
The group B meningococcal polysaccharide is isolated from N. meningitidis by methods which are known in the art. In one such method, group B meningococci (strain 981B) were grown at 37xc2x0 C. in a fermenter using 30 g. of dehydrated Todd Hewitt Broth (Difco Laboratories, Detroit, Mich.) per liter of distilled water. Prior to fermenter growth, the lyophilized strain was grown initially in a candle jar at 37xc2x0 C. on 5% (v/v) Sheeps"" Blood Agar (Difco Laboratories, Detroit, Mich.) plates. The bacteria were then transferred to 1.0 liter of Todd Hewitt Broth (as above) in an Erlenmeyer flask which was shaken at 37xc2x0 C. for 7 hours at 190 r.p.m. This inoculum was then transferred to the fermenter. After fermenter growth (16 hours) the bacteria were killed by the addition of formalin to a final concentration of 0.75%. The bacteria were removed by continuous centrifugation and the group B meningococcal polysaccharide was isolated from the supematant and purified essentially as described by Bundle et al, J. Biol. Chem., 249, 4797-4801 (1974) except that the protein was extracted by stirring a solution of the crude polysaccharide with cold (4xc2x0 C.) 90% phenol instead of hot (50-60xc2x0 C.). This latter process ensures that a high molecular weight form of the GBMP is produced.
E. coli (018:K1:H7) (NRCC 4283) were grown at 37xc2x0 C. in a fermenter in distilled water containing dehydrated Brain Heart Infusion (BHI; 37 g/liter) (Difco Laboratories, Detroit, Mich.). Prior to fermenter growth, the lyophilized strain was grown on 50 ml of BHI solution (same as above) in an Erlenmeyer flask which was shaken at 37xc2x0 C. for 7 hours at 200 r.p.m. This growth was then transferred to 1.5 liters of BHI (as above) and grown under the same conditions as described above for 7 hours. The inoculum was then transferred to the fermenter.
The procedure employed in the isolation and purification of the capsular polysaccharide of E. coli K1 were identical to those described above for the isolation of the group B meningococcal polysaccharide.
It will be appreciated that the isolation and purification procedures described above are not the only ones which may be utilized, and that other published procedures are available, for example those described by Watson et al, J. Immunol. 81, 331 (1958) and in the above-mentioned U.S. Pat. No. 4,727,136.
The native polysaccharide is N-deacetylated to provide a reactive amine group in the sialic acid residue parts of the molecule. The N-deacetylation can be carried out by any known method, for example in a basic aqueous medium at elevated temperatures, for example about 90xc2x0 to 110xc2x0 C., and at a pH of about 13 to 14. The basic aqueous medium is suitably an aqueous alkli metal hydroxide solution, for example sodium hydroxide of about 2M concentration. Alternatively, hydrazine in aqueous solution may be used. The degree of N-deacetylation may vary from about 30% to 100% depending on the conditions. It is preferred to achieve about 90 to 100% N-deacetylation. N-deacetylated product can be recovered for example by cooling, neutralizing, purification if desired, and lyophilization.
As a result of N-deacetylation, fragments of the polysaccharide are usually produced having an average molecular weight ranging from about 3,000 to 50,000 Daltons. For use in this invention, fragments or full length polysaccharides may be used.
The N-deacetylated polysaccharide fragments or full length polysaccharides are then N-acylated to produce the corresponding N-acylated product. The N-acylation may be carried out by dissolving the N-deacetylated polysaccharide in an aqueous buffered medium having a pH of about 7.5 to 9.0, followed by adding the appropriate unsaturated acyl anhydride, optionally with an alcohol to increase solubility, and cooling to below 10xc2x0 C. until the reaction is complete. If desired, the reaction medium can be purified. Non-limiting examples of purification methods which may be utilized include dialysis followed by recovery of the N-acylated product by lyophilization. The reaction is substantially complete within about 10 to 20 hours. The degree of N-acylation, as measured by analytical techniques, typically 1H nmr, is at least 90% and more likely close to 100%. The N-acylation reaction does not result in any significant molecular weight reduction of the fragments.
The conjugate molecules of this invention have at least one group B Neisseria meningitidis polysaccharide wherein the N-acetyl group is substituted with an unsaturated N-acyl group of formula II 
wherein R2 is an unsaturated C2-4 alkyl group. The conjugates therefore may comprise the unsaturated polysaccharides of this invention and may also include the acryloyl derivative.
It is preferred, according to the present invention, to select for conjugation purposes the C3-5 N-acylated material having an average molecular weight corresponding to about 10 to 200 sialic acid residues. Thus, a preferred conjugate is the N-acryloyl (2-propeneoyl) derivative. This is generally achieved by way of gel filtration of the N-acylated GBMP using an Ultragel(copyright) AcA 44 (Bead diameter 60-140 um) column, using PBS as eluant. Alternatively, a suitable sizing membrane may be employed.
Unsaturated N-acylated material of average molecular weight of 10,000 to 15,000 Daltons, is preferably employed for the invention. This is obtained by collecting the fractions of the eluant of the column containing N-acylated GBMP material having that average molecular weight range. N-acylated material of higher average molecular weight, for example in the region of 30,000 to 40,000 Daltons, has also proved to be useful according to the invention.
The molar ratio of polysaccharide to protein in the conjugate molecules of the invention is preferably between 1 mole protein to 20 moles polysaccharide. More preferably the ratio is between 1 mole protein and about 2-15 mole polysaccharide. Most preferably the ratio is about 1 mole protein and 4 to 7 moles polysaccharide. Variations in protein/polysaccharide ratio may be achieved by adjusting the ratio of the starting components in the conjugation reaction.
In addition to providing conjugate molecules comprising unsaturated N-acyl derivative polysaccharides conjugated to protein, this invention also contemplates multivalent conjugates and their vaccines wherein different types of polysaccharides are conjugated to a single protein.
The vaccines of the invention are produced by conjugating the unsaturated N-acylated polysaccharide with an immunologically suitable carrier protein. Preferably, the carrier protein itself is an immunogen. Non-limiting examples of suitable carrier proteins are bacterial proteins, or polypeptides including tetanus toxoid, diphtheria toxoid, cross-reacting materials (CRMs), preferably CRM197xe2x80x2 (obtained from Sclavo Ltd., Siena, Italy), and bacterial protein carriers, such as meningococcal outer membrane proteins.
Any mode of conjugation may be employed to conjugate the modified polysaccharide fragments with the carrier protein. A preferred method is that described in U.S. Pat. No. 4,356,170, i.e. by introducing terminal aldehyde groups (via oxidation of cis-vicinal hydroxyl groups) into the N-acylated polysaccharide and coupling the aldehyde groups to the protein amino groups by reductive amination. The polysaccharide and the protein are thereby linked through a xe2x80x94CH2xe2x80x94NHxe2x80x94protein linkage.
It is to be understood, however, that the conjugate vaccines of the invention are not limited to those produced via reductive animation. Thus, the vaccines may also be produced by conjugating the N-acylated polysaccharide with the carrier protein using an adipic dihydrazide spacer, as described by Schneerson, R., et al, Preparation, Characterization and Immunogenicity of Haemophilus influenzae type b Polysaccharide-Protein Conjugates, J. Exp. Med., 1952, 361-476 (1980), and in U.S. Pat. No. 4,644,059 to Lance K. Gordon. Alternatively, the binary spacer technology developed by Merck may be used, as described by Marburg, S., et al, xe2x80x9cBiomolecular Chemistry of Macromolecules: Synthesis of Bacterial Polysaccharide Conjugates with Neisseria meningitidis Membrane Proteinxe2x80x9d, J. Am. Chem. Soc., 108, 5282-5287 (1986) or, possibly, the reducing ends methodology.
The conjugate molecules prepared according to this invention typically comprise a protein to which is bound at least one meningococcal polysaccharide fragment of the present invention through a single binding site at the terminal end of the backbone of the polysaccharide fragment. Thus, this invention provides the ability, if desired, to produce, meningococcal conjugate molecules wherein the polysaccharide component, except for one end, is unobscured by protein. Other methods of conjugating meningococcal polysaccharides to protein through the terminal sialic acids of the branches may, result in crosslinking, and attachment of polysaccharide to protein at a plurality of sites. This invention also contemplates conjugate molecules which may be made using a combination of methods.
The resulting N-acylated polysaccharide protein conjugates which do not possess significant cross-linking are soluble in aqueous solutions. This makes these conjugates of the invention particularly good candidates for vaccine use.
A resulting unsaturated N-acylated-polysaccharide protein conjugate of the invention has been tested in in vitro tests in mice, and has been shown to possess improved immunogenic properties as compared with the N-propionylated-polysaccharide. In addition, substantially reduced formation of cross-reactive antibodies is observed. In addition, the unsaturated conjugate demonstrated unexpected high bactericidal titers compared to other conjugates tested. In light of this, it is believed that the vaccines of the invention will be useful against meningitis caused by group B N. meningitidis or by E. coli K1 organisms. Of particular interest are vaccines for protecting human infants who are most susceptible to bacterial meningitis.
The vaccines of this invention may comprise standard carriers, buffers or preservatives known to those in the art which are suitable for vaccines. In addition, adjuvants such as alum or stearyl tyrosine may also be included in the formulation to enhance the immunogenic response.
The vaccines of the present invention are typically formed by dispersing the conjugate in any suitable pharmaceutically acceptable carrier, such as physiological saline or other injectable liquids. The administration of the vaccine of the present invention may be effected by any of the well-known methods, including, but not limited to subcutaneously, intraperitonealy or intramuscularly. The preferred method of administration of the vaccine is parenteral administration. Additives customary in vaccines may also be present, for example stabilizers such as lactose or sorbitol and adjuvants such as aluminum phosphate, hydroxide, or sulphate.
The vaccines of the present invention are administered in amounts sufficient to provoke an immunogenic response. Typically a dose of between about 1 and 50 gg polysaccharide is effective for generating such a response. Dosages may be adjusted based on the size, weight or age of the individual receiving the vaccine. The antibody response in an individual can be monitored by assaying for antibody titer or bactericidal activity and boosted if necessary to enhance the response.
A suitable dosage for the vaccine for human infants is generally within the range of about 5 to 25 micrograms, or about 1 to 10 micrograms per kilogram of body weight.